1. Field of the Invention
This invention relates generally to scanning beam antennas and more particularly a fixed antenna that generates a scanning beam useful for radar and communication system applications.
2. Prior Art
Known scanning antennas heretofore included phase shifting antennas utilizing ferrite materials. One such phase shifting device is disclosed in U.S. Pat. No. 4,691,208. This device includes a ferrite plate surrounding a dielectric waveguide.
Generally, ferrite phase shifters are readily adaptable into antenna systems at microwave frequencies up to 20 GHz. Above that frequency, they are not particularly usable. Limitations of ferrite phase-shifting antennas include requiring a substantial power input to effect a phase change, high insertion loss, and requiring circuity not easy to integrate.
An electronic scanning antenna is shown in U.S. Pat. No. 4,667,201. While this antenna provides a wide range of scanning angles, its phase shifter is expensive especially in millimeter wave frequencies.
Another scanning array antenna is described in a paper authored by M-Y Li, S. Kanamalura, and K. Chang, entitled, Aperture-Coupled Microstrip Antenna Array Fed By Dielectric Image Line, and published in Electronics Letters, pp. 1105-1106, Vol. 30, No. Jul. 14, 1994. Structure of the discussed antenna is quite simple. In this case, the required phase shifting is effected by operating at different frequencies. Frequency scanning antennas have several limitations, however. First, the frequency bandwidth must be quite wide to obtain an effective scanning angle range. However, the needed frequency bandwidth may not comply with frequency bandwidth uses established by the Federal Communication Commission (FCC). Secondly, frequency scanning antennas cannot be used with radar or communication systems utilizing frequency modulation mechanisms.
Another scanning array antenna is disclosed in U.S. Pat. No. 5,504,466. This antenna uses a suspended dielectric and microstrip type microwave phase shifter. While this phase shifter can be easily integrated with other circuitry, there are substantial fabrication costs. These higher costs relate to needs for a large microwave laminate for the antenna substrate and special dielectric materials for the phase shifter. Also, this antenna is inefficient because of high circuit loss in the microstrip power splitter and phase shifter.